class Solution {
public:
    bool vis[7][7];
    int m, n;
    int dx[4] = { 0, 0, 1, -1 };
    int dy[4] = { 1, -1, 0, 0 };

    bool exist(vector<vector<char>>& board, string word) {
        m = board.size();
        n = board[0].size();
        for (int i = 0; i < m; i++)
        {
            for (int j = 0; j < n; j++)
            {
                if (board[i][j] == word[0])
                {
                    vis[i][j] = true;
                    if (dfs(board, i, j, word, 1)) return true;
                    vis[i][j] = false;
                }
            }
        }

        return false;
    }

    bool dfs(vector<vector<char>>& board, int i, int j, string& word, int pos)
    {
        if (pos == word.size())
            return true;

        for (int k = 0; k < 4; k++)
        {
            int x = dx[k] + i, y = dy[k] + j;
            if (x < m && y < n && x >= 0 && y >= 0 && board[x][y] == word[pos] && !vis[x][y])
            {
                vis[x][y] = true;
                if (dfs(board, x, y, word, pos + 1)) return true;
                vis[x][y] = false;
            }
        }

        return false;
    }
};